What credit defaults are used for are to insure the debt of a commpany.

In the case of BP, their cost to insure their debt increased by 106 basis points to 368 basis points, which means it costs them $368,000 a year now to insure every $10 million they are in debt for, according to Markit Intraday.

These three companies are probably the most at risk in the accident, with BP owning 65 percent of the oil well, Anadarko 25 percent, and Transocean being the company who had operational responsibility for the Deepwater Horizon oil rig.